Surgical Knife Safety Handle Having User Operable Lock

ABSTRACT

A surgical knife safety device having a handle, a blade connected to the handle, and a guard carried by the handle for sliding movement between a retracted position in which the blade is exposed for use, and an extended position for covering the sharp cutting edge of the blade. A spring, such as leaf spring or a cantilever beam, and a pair of detents or slots are provided to fix the guard in the extended or retracted position and to provide resistance during movement between the two positions.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 15/335,655entitled “Surgical Knife Safety Handle Having User Operable Lock,” filedOct. 27, 2016, now U.S. Pat. No. 10,357,279, which is a continuation ofU.S. patent application Ser. No. 14/337,191 entitled “Surgical KnifeSafety Handle Having User Operable Lock,” filed Jul. 21, 2014, now U.S.Pat. No. 9,480,495, which is a continuation of U.S. patent applicationSer. No. 12/929,008, filed Dec. 22, 2010, now U.S. Pat. No. 8,814,893entitled “Surgical Knife Safety Handle Having User Operable Lock,”issued Aug. 26, 2014, which is a continuation of U.S. patent applicationSer. No. 11/252,575, filed Oct. 19, 2005, now U.S. Pat. No. 7,909,840entitled “Surgical Knife Safety Handle Having User Operable Lock,”issued Mar. 22, 2011, which claims the benefit under 35 U.S.C. § 119(a)of U.S. Provisional Application No. 60/619,958 entitled “Surgical KnifeSafety Handle Having User Operable Lock,” filed Oct. 20, 2004. Theentire contents of all of said prior applications are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a system and method for a surgicalknife safety handle, for both ophthalmic and non-ophthalmicapplications, having a movable guard that can be retracted to expose theblade when in use, and that can be extended to cover the blade when notin use, and including a pushback prevention mechanism and a useroperable lock to ensure that the blade is covered until manuallyexposed.

BACKGROUND OF THE INVENTION

In various surgical procedures, the surgeon typically has to make anincision in the patient in order to remove unwanted tissue, repairdamaged tissue, or implant a device to improve the patient's well being.In certain cases, all three of these activities, or a combinationthereof, must be done in a single procedure. For example, in cataractsurgery, the surgeon removes the natural lens that has been clouded by acataract from the patient's eye and replaces it with an artificial lensthat will improve the patient's eyesight. In order to perform thisprocedure, an incision is made in the cornea of the eye by the surgeonusing a scalpel. This provides the surgeon with access to the patient'slens. The clouded lens is cut loose and removed. There are a number ofdifferent procedures that are used to remove a patient's lens that has acataract. Two of the more common techniques are known as extracapsularsurgery and phacoemulsification.

In extracapsular surgery, the surgeon removes the lens leaving behindthe back half of the capsule. In phacoemulsification, the surgeonfragments the lens by ultrasonic vibrations and the lens issimultaneously irrigated and aspirated. After the lens is removed, thesurgeon then inserts an artificial lens known as an intra-ocular lens(IOL) into the eye either behind or in front of the iris. Two smallC-shaped arms connected to the IOL eventually become scarred into theside of the eye and hold the IOL firmly in place.

In another type of ophthalmic procedure known as the Implantable ContactLens procedure (ICL), the surgeon makes an incision in the patient's eyeand implants a contact lens in the eye in front of the existing lens butbehind the iris. This corrects the patient's vision so that he or shecan see clearly without the need for external contact lenses oreyeglasses.

Typically a nurse or other surgical assistant manages the devices thatare used during such delicate surgeries. For example, the assistantensures that the appropriate sterile devices are available in theoperating suite for the particular procedure that is to be performed.With respect to scalpels, the assistant often hands the scalpel to thesurgeon in a predetermined orientation so that the surgeon can grip thescalpel's handle without taking his or her eyes away from the patient.This also minimizes the possibility that the surgeon will be cut withthe blade on the scalpel. After the surgeon completes the incision, thescalpel is handed back to the assistant for proper disposal orsterilization. While the procedure is being performed, this requires theassistant to place the used scalpel on a particular tray that will beremoved after the procedure is completed. The devices on the tray arethen disposed of or are sterilized for reuse.

If all appropriate protocols are followed, no hospital personnel will becut by used or unused scalpel blades. Unfortunately, accidental cuts ofhospital personnel do occur for a variety of reasons. For example,because the surgeon and assistant are concentrating on the patient andthe procedure being performed on the patient, they may not pay closeattention to the scalpels. Also, the scalpels may become exposed duringshipment or when scalpel packages are dropped or mishandled prior touse. Once opened, the assistant may put the used scalpels in aninappropriate location or, even if the used scalpels are placed on theproper tray, the blade may be exposed to the operating suite personnel.In these situations, the operating suite personnel may inadvertentlycome into contact with the blade as they move around the patient duringthe procedure and be cut or nicked by the exposed blade.

Other hospital personnel may also come into contact with such blades andmay also be cut or nicked. Usually used blades are disposed of in anappropriate sharps container that allows used needles and blades to beinserted into the container but prevents access by hospital personnel tothe sharp end of a needle or the sharp cutting surface of the blade.However, during cleanup of the operating suite, the used blades may beexposed prior to their placement in the appropriate sharps container. Ifhospital personnel are not paying close attention to their activitiesor, if the exposed blades are hidden from view because they are buriedin a pile of other devices or hospital linen, these hospital personnelmay come into contact with the sharp cutting surface of the blade and becut or nicked.

Cuts and nicks from blades are uncomfortable and distracting at best. Inaddition, such cuts and nicks from used blades may result in blood orbody fluid exposure which can result in the spread of infectiousdiseases between the patient and hospital personnel. Concern over thissituation has become especially acute in recent years because of suchdiseases as acquired immuno-deficiency syndrome, i.e. AIDS, andhepatitis. These diseases may be transmitted from an infected person toanother person by the transmission of body fluids, typically blood.

In view of the need for a scalpel that can at least minimize the chancesof accidental cuts or nicks, while also protecting the cutting edge ofthe blade, numerous scalpels have been designed. These designs typicallytake the form of a scalpel having a guard that shields the sharp cuttingsurface of the blade from undesired contact with hospital personnel andsurrounding surfaces. The guard in these devices can be extended to aposition shielding the blade or retracted exposing the blade for use.Alternatively, the scalpel may be designed to allow the blade to moveinto or out of the scalpel handle, to either shield or expose the sharpcutting surface.

Unfortunately, these designs are deficient because they tend to becumbersome and difficult to use, and because they may cause unwantedshielding or exposure of the blade prior to the need for such shieldingor exposure. Also, such devices may require considerable attention bythe user to shield or expose the blade. Additionally, the shield maydistort the handle outline when retracted, making the handle difficultto hold or control. Any design which allows the blade to move, forretraction or extension design purposes, also introduces concernsregarding exact blade positioning and rigidity during use. Such concernsalso apply in cases in which the user is required to hold the retractedshield as a grip, allowing any movement between shield and handle topossibly result in unwanted movement of the blade.

Accordingly, a need exists for a device and method to provide ashielding mechanism that is simple to use and remains in a shieldingposition until disengaged by the user, even during shipping and whenmishandled or dropped prior to opening. The handle and shieldingmechanism should also provide a uniform gripping surface when retracted,allowing user control of the scalpel without any unwanted grippingsurface or blade movement.

SUMMARY OF THE INVENTION

It is therefore an object of embodiments of the present invention toprovide a device and method that may be used to shield and protect asharp blade, such as a scalpel, and minimize the chances of cuts ornicks during shipping, handling or disposal.

It is another object of embodiments of the present invention to providea device and method that is easy to use and that can be operated by onehand of the user.

It is another object of embodiments of the present invention to providea device and method that will substantially prevent the shield frombecoming accidentally displaced when fully extended and exposing theblade.

It is another object of embodiments of the present invention to providea device and method that will substantially prevent the shield frombecoming accidentally displaced and exposing the blade during shipping.

It is another object of embodiments of the present invention to providea device and method that will substantially prevent the shield frombecoming accidentally displaced and exposing the blade duringmishandling when packaged.

It is another object of embodiments of the present invention to providea device and method comprising a pushback prevention mechanism that willsubstantially prevent the shield from becoming accidentally displacedand exposing the blade when a force is applied to the fully extendedshield.

It is another object of embodiments of the present invention to providea device and method comprising a user operable lock that willsubstantially prevent the shield from becoming accidentally displacedand exposing the blade until intentionally released by a user.

It is another object of embodiments of the present invention to providea device and method comprising a drop-force operable lock that willsubstantially prevent the shield from becoming accidentally displacedand exposing the blade when a drop force or impact force is applied tothe device end opposite to the shield.

It is another object of embodiments of the present invention to providea device and method that will allow the user to manually release theuser operable lock securing the shield and retract the shield to exposethe blade with a single hand.

It is another object of embodiments of the present invention to providea device and method which maintains an uninterrupted handle surfacecontour during use, which allows the user better control and orientationof the device.

These and other objects are substantially achieved by providing, inaccordance with embodiments of the present invention, a devicecomprising a handle, a blade connected to the handle, and a guardslidably mounted partially within the handle for sliding movementbetween a retracted position in which the blade is exposed for use, andan extended position for covering the sharp cutting edge of the blade.In the retracted position, an exposed guard radius is provided at thedistal end of the handle to allow improved handle control and bladeorientation. The exposed guard radius however, is positioned to allowthe user to firmly grip a large distal handle portion which is molded asa single piece with the blade holder, preventing unwanted blade orhandle movement due to guard mechanism tolerances.

In accordance with embodiments of the present invention, a leaf springor cantilever beam, and detents are provided to fix the guard in theextended and retracted position, and to provide slight resistance duringmovement between each position. Additionally, a pushback preventionmechanism and a user operable lock are incorporated with the guard toprevent accidental retraction from the fully extended position. Thepushback prevention mechanism comprises a conical surface slidablypositioned within a collet-like guard opening to expand under certainconditions and prevent guard displacement when fully extended exceptthrough drive mechanism control. The user operable lock comprises acantilever beam and projection for engagement with a handle body detentto substantially secure the guard in a fully extended position untilintentionally released by the user. The drop-force operable lock can beprovided as a rod and button extending from the proximal end of thedevice to transfer any drop force or impact force to the guard toprevent guard movement. The above and other objects and advantages ofthe present invention will be apparent upon consideration of thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages will become apparent uponconsideration of the following drawings and detailed description. Thepreferred embodiments of the present invention are illustrated in theappended drawings in which like reference numerals refer to likeelements and in which:

FIG. 1 is a perspective view of an embodiment of the present inventionwith the guard in a retracted position to expose the blade;

FIG. 2 is a perspective view of the embodiment of FIG. 1 with the guardin an extended position to shield the blade;

FIG. 3A is an exploded perspective view of the embodiment of FIG. 1;

FIG. 3B is a side view of another version of the lower body contour wallhaving different sized detent openings in accordance with an embodimentof the present invention;

FIG. 3C is a cross-sectional view of the lower body contour wall of FIG.3B illustrating a path between detent openings;

FIG. 4 is a cross-sectional view of the embodiment of FIG. 1 taken alongline A-A of FIG. 1;

FIG. 5A is a perspective view of an embodiment of the engagement betweenthe guard positioning mechanism and the guard in accordance with anembodiment of the present invention;

FIG. 5B is a cross-sectional view of the embodiment of the engagementend of the guard in FIG. 5A;

FIG. 5C is an elevational view of the embodiment of the engagement endof the guard in FIG. 5A;

FIG. 5D is a cross-sectional view of the embodiment of the engagementend of the guard positioning mechanism in FIG. 5A;

FIG. 5E is an elevational view of an embodiment of the engagement end ofthe guard positioning mechanism in FIG. 5A;

FIG. 6 is an enlarged cross-sectional view of the embodiment of theguard positioning mechanism and the guard of FIG. 5A taken along lineB-B of FIG. 1;

FIG. 7 is an enlarged cross-sectional view of the embodiment of theguard positioning mechanism and the guard of FIG. 5A taken along lineC-C of FIG. 1;

FIG. 8A is a cross-sectional view of a second version of the embodimentof FIG. 1 illustrating a guard positioning mechanism having an integralspring;

FIG. 8B is an enlarged cross-sectional view of the detent engagement ofthe integral spring of FIG. 8A;

FIG. 8C is an enlarged cross-sectional view of the detent engagement ofthe leaf spring of FIG. 3A;

FIG. 8D is an elevational view of the guard positioning mechanism andintegral spring of FIG. 8A;

FIG. 8E is a bottom view of the guard positioning mechanism and integralspring of FIG. 8A;

FIG. 8F is a perspective view of the guard positioning mechanism andintegral spring of FIG. 8A;

FIG. 8G is an exploded perspective view of another embodiment of thepresent invention further illustrating a user operable lock;

FIG. 8H is a cross-sectional view of the guard positioning mechanism anduser operable lock of FIG. 8G in a locked position in accordance with anembodiment of the present invention;

FIG. 8I is a cross-sectional view of the guard positioning mechanism anduser operable lock of FIG. 8G;

FIG. 8J is a perspective view of the guard positioning mechanism anduser operable lock of FIG. 8G;

FIG. 8K is a top view of the guard positioning mechanism and useroperable lock of FIG. 8G;

FIG. 8L is a cross-sectional view of the guard positioning mechanism anduser operable lock of FIG. 8G;

FIG. 9A is a perspective view of another embodiment of the presentinvention with the guard in a retracted position to expose the blade;

FIG. 9B is a perspective view of the embodiment of FIG. 9A with theguard in an extended position to shield the blade;

FIG. 10 is an exploded perspective view of the embodiment of FIG. 9A;

FIG. 11 is an enlarged cross-sectional view of the embodiment of FIG. 9Ataken along line D-D of FIG. 9A;

FIG. 12A is a perspective view of another embodiment of the presentinvention with a plunger type operator control and the guard in anextended position to shield the blade;

FIG. 12B is a perspective view of the embodiment of FIG. 12A with aplunger type operator control and the guard in a retracted position toexpose the blade;

FIG. 12C is a perspective view of another embodiment of the presentinvention with a segmented plunger type operator control and the guardin a retracted position to expose the blade;

FIG. 13A is a cross-sectional view of another embodiment of the presentinvention with a drop-force operable lock;

FIG. 13B is a view of an alternate contact button shape for theembodiment of FIG. 13A; and

FIG. 13C is a view of another alternate contact button shape for theembodiment of FIG. 13A.

In the drawing figures, it will be understood that like numerals referto like structures.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The embodiments of the present invention described below comprise asurgical knife safety handle, for both ophthalmic and non-ophthalmicapplications, having a movable guard that can be retracted to expose theblade when in use, and that can be extended to cover the sharp cuttingedge of the blade when not in use. The guard is located at a distal endof the handle, partially extending from inside the handle, and includinga larger diameter shielding end which becomes part of the exposed handlewhen fully retracted. When fully extended, the guard covers the exposedcutting edge of the blade without distorting handle contours. The guardis engaged with a drive mechanism slidably mounted within the handlebody, which includes a leaf spring or flexible cantilever beam forengaging detents at fully extended and fully retracted positions, andproviding audible and tactile engagement feedback. The engagementbetween the guard and drive mechanism also includes a pushbackprevention mechanism comprising a conical surface slidably positionedwithin a collet-like guard opening to substantially prevent guarddisplacement when fully extended except through drive mechanism control.Additionally, embodiments of the present invention can further include auser operable lock between the guard drive mechanism and the handle bodyto substantially prevent undesired guard drive mechanism movement, suchas undesired movement occurring during shipment or package mishandling.Still further, embodiments of the present invention can include adrop-force operable lock to substantially prevent undesired guard drivemechanism movement when a sudden force or impact is applied to a deviceend opposite the guard.

As shown in FIG. 1, the surgical knife safety handle 10 of a firstembodiment of the present invention includes a body 20 having a guard 30slidably received partially within body 20 for longitudinal slidingmovement between a retracted and extended position. FIG. 1 is aperspective view of an embodiment of the present invention with theguard 30 in a retracted position to expose a blade 40 for use. The guard30, when in the retracted position, forms a smooth, uninterrupted handlesurface between distal and proximal ends, which is preferred by users ofsuch devices when in use. Additionally, the enlarged guard portion,external to body 20 when fully retracted, defines a noncircular contourabout the distal end of the surgical knife safety handle 10 which givesthe user better control and allows easier blade orientation during use.

As used herein, the term “proximal” refers to a location on the surgicalknife safety handle 10 closest to the person using the device handle andfarthest from the patient in connection with which the device handle isused. Conversely, the term “distal” refers to a location on the devicehandle of this invention farthest from the person using the devicehandle and closest to the patient in connection with which the devicehandle is used.

The surgical knife safety handle 10 of the present invention alsoincludes a blade 40, or similar device, fixedly secured to the distalend of body 20. However, as stated earlier, exposed blades such as thispresent several hazards, including accidental cuts of hospital personneland blade damage. To prevent this, the guard 30 can be slideablyextended from the distal end of body 20 to shield the exposed blade 40as shown in FIG. 2. FIG. 2 is a perspective view of the embodiment ofFIG. 1 with the guard 30 in an extended position. A leaf spring andpushback prevention mechanism is employed within the body 20 to preventunwanted movement of the guard 30 when fully extended, as described ingreater detail below.

FIG. 3A is an exploded perspective view of the embodiment of FIG. 1. Theview of FIG. 3A includes an upper body contour wall 22 and a lower bodycontour wall 24, formed to assemble as a handle body 20 and define asubstantially hollow chamber within the body 20 to house a guardpositioning mechanism 50 and a concealable portion of the guard 30.

The upper body contour wall 22 includes a slot 28 accessing the chamberto allow protrusion of a raised operator control 58 for the guardpositioning mechanism 50, which can be collectively referred to as auser actuator. The upper body contour wall can further include a detent(not shown) for use with a user operable lock to ensure that the bladeremains covered until manually exposed. An exemplary embodiment of theuser operable lock is described in greater detail below with referenceto FIG. 8G.

The distal end of the upper body contour wall 22 also includes an outersurface having a dimpled texture, extending from the distal end of theupper body contour wall 22 to a point slightly before the access slot28. The textured surface is sufficient to provide the user with anonslip grip during use, and is duplicated in a similar position on thelower body contour wall 24 such that when assembled, the texturedsurface appears uniform about an outside diameter of the body 20 nearthe distal end. Although a dimpled surface is shown in the embodiment inFIG. 3A, any nonslip surface can be used. Additionally, the nonslipsurface can be extended or modified from the area shown and described inFIG. 3A as required in other embodiments.

The distal end of the upper body contour wall 22 further includes asemicircular mating port, extending rearward from the distal end, andproviding a position in which the raised contoured surface of theexposed portion of the guard 30 is seated when fully retracted. In thefully retracted position, the mating port and exposed guard portion ofthe guard 30 are configured to provide the smooth, uninterrupted handlesurface and noncircular contour about the distal end as described above.

The upper body contour wall 22 and lower body contour wall 24 assembleto form the handle body 20 and define a substantially hollow chamberwithin the body 20 to house a guard positioning mechanism 50 and aconcealable portion of guard 30. The guard positioning mechanism 50,which is described in greater detail below and shown in FIG. 5A, has agenerally cylindrical cross section and is sized to slidably fit withinthe hollow chamber within the body 20. The guard positioning mechanism50 is controlled to travel between a fully extended and fully retractedposition via an external protrusion 58 accessed through channel 28. Eachposition is maintained by an engagement between a leaf spring 52, whichis contained within a body cavity of the guard positioning mechanism 50,and either a first or second detent 54 and 56 in the lower body contourwall 24 as described below. In another embodiment of the presentinvention described in greater detail below, the guard positioningmechanism 50 further includes a user operable lock to assist inmaintaining the guard in a fully extended position. In still anotherembodiment of the present invention described in greater detail below,the guard positioning mechanism 50 further includes a drop-forceoperable lock to assist in maintaining a fully extended position.

The lower body contour wall 24 includes a first and second detent 54 and56 to engage the leaf spring 52 of the guard positioning mechanism 50,locking the guard in position when fully extended or fully retracted. Asnoted above, the upper body contour wall 22 and lower body contour wall24 assemble to define a substantially hollow chamber within the body 20to house the guard positioning mechanism 50 which contains a leaf spring52, wherein the leaf spring is oriented within the guard positioningmechanism 50 to firmly press against the lower body contour wall 24 whensliding between extended and retracted positions. The lower body contourwall 24 includes first and second detents 54 and 56, located at oppositepositions within the substantially hollow chamber such that the leafspring engages the first detent 54 when the guard positioning mechanism50 is in a fully retracted position, and engages the second detent 56when the guard positioning mechanism 50 is in a fully extended position.Slidable movement of the guard positioning mechanism 50 betweenpositions is opposed with a slight resistance created by the leaf spring52 contact with the lower body contour wall 24 between detents.

The detents 54 and 56 can be provided as substantially similar shapedand sized slots in the lower body contour wall 24 as shown in FIG. 3A,or can have varying sizes and dimensions, as shown by the detents 55 and57 in the lower body contour wall example 25 in FIGS. 3B and 8G. FIG. 3Bis a side view of another version of the lower body contour wall havingdifferent sized detent openings, and FIG. 8G is an exploded perspectiveview including the lower body contour wall 25 of FIG. 3B in accordancewith another embodiment of the present invention. The smaller detent 57can be provided to establish a positive engagement force with the leafspring or an integral cantilever beam as described in greater detailbelow. As the detent 57 corresponds to the guarded position, the detentopening can be constructed having a smaller opening which engages thespring or beam more securely, that is, holding the spring or beam in aslightly deflected and tensed position, and providing a positive lockingforce for the guarded position. The detent 55 corresponds to theunguarded, or retracted position and therefore, can be provided having alarger opening. The larger opening of the detent 55 ensures that thespring or beam is more relaxed when engaged and does not take a “set”when in the retracted position. Also, variations in detents 55 and 57allow for establishing different activation forces required to extendand retract the guard positioning mechanism 50.

The engagement between spring and either detent also provides audibleand tactile engagement feedback to the user. The engagement produces anaudible sound, such as a “click”, when fully extended or fullyretracted, and the spring is properly engaged. Also, the properengagement also produces a mechanical vibration pulse, or tactilefeedback, which allows the user to ensure engagement has occurred.

As shown in FIG. 3A, the distal end of the lower body contour wall 24also includes a tapered blade holder 26, or post, configured to fixedlysecure the blade 40 to the distal end of body 20. The tapered bladeholder 26 is molded as an extension of the lower body contour wall 24distal end and has a generally circular cross section area at a point ofattachment, and is tapered slightly to a reduced cross section area at apoint of attachment to the blade 40, which can be epoxy bonded to thetapered blade holder. Additional details of blade attachment aredisclosed in U.S. patent application Ser. No. 10/835,286, the entiredisclosure of which is incorporated herein by reference.

As shown in FIG. 4, the tapered blade holder 26 is secured to the lowerbody contour wall 24 distal end via a molded connection spanningapproximately 90 degrees of the circumference of the generally circularcross section area of the tapered blade holder 26 at the point ofattachment, allowing the guard 30 to effectively shield approximately270 degrees about the axis of the blade when fully extended. FIG. 4 is across-sectional view of the embodiment of FIG. 1 taken along line A-A ofFIG. 1, showing the point of attachment between the tapered blade holder26 and the lower body contour wall 24, and the semicircular opening atthe distal end of the body 20 through which the guard is extended andretracted during use. The cross section shown in FIG. 4 also shows theenlarged distal end of the guard 30, which is required to providesufficient clearance for the blade when fully extended. This enlargeddistal end is shown as one example, an may be modified to accommodateany blade type or guarding purpose.

In FIG. 4, the molded connection between the tapered blade holder 26 andthe lower body contour wall 24 provides a first and second slot 27 a and27 b on either side of the holder 26, for use in guiding the guard 30between extended and retracted positions and preventing twisting ordistortion. As additional support for the guard 30, the assembly of bodycontour walls 22 and 24 creates a third slot 27 c between contour wall22 and the tapered blade holder 26, linking slots 27 a and 27 b, suchthat a continuous semicircular slot is provided at the distal end, aboutthe tapered blade holder 26, through which the guard 30 travels betweenfully extended and fully retracted positions. The guard 30, as describedin greater detail below, has a generally semicircular cross section andis sized at a proximal end to extend and retract through thesemicircular distal opening provided by the body 20, and is enlarged ata distal end to surround the blade 40 without interference whenextended. The guard 30 can be constructed of any suitable material,including transparent or opaque polycarbonate materials. A transparentguard is advantageous in allowing the user to see the blade 40 even whenit is fully shielded by the guard.

In the first embodiment of the present invention shown in FIG. 1, theguard 30 does not have a fully circular cross section at the distal enddue to the molded attachment of the tapered blade holder 26 to the lowerbody contour wall 24. This feature ensures the user is allowed to firmlygrip a surface that is singularly molded with the blade holder 26. Thispresents a more positive grip which is less susceptible to unwantedblade or gripping surface movements due to tolerances between the guard30 and each body contour wall 22 and 24. The enlarged distal end of theguard 30 which remains external to the body 20 when fully retractedhowever, is rigid enough to provide additional control and bladeorientation with one or more fingers of the user if so desired duringuse.

FIGS. 5A-5E, 6 and 7 show additional details of the guard positioningmechanism 50, the guard 30, and the pushback prevention mechanismtherebetween. FIG. 5A illustrates the engagement between the guardpositioning mechanism and the guard, and FIGS. 6 and 7 illustrate anenlarged cross-sectional view of the engagement shown and described inrelation to the body 20. FIGS. 5B-5E provide additional views of theengagement mechanisms of both the guard positioning mechanism and theguard.

As shown in FIG. 5A, the guard positioning mechanism 50 has a generallycircular cross section and is sized to slidably fit within the hollowchamber within the body 20. The guard positioning mechanism 50 ismechanically engaged with the guard 30 to direct and control guardtravel between a fully extended and fully retracted position. Thecombined length of the mechanism 50 and guard 30 is sufficient to allowa substantial portion of the guard 30 to retract within body 20. Only apartial radius of the enlarged distal end of the guard 30 remainsexposed as shown in FIG. 1.

The guard positioning mechanism 50 is mechanically engaged with theguard 30 via a pushback prevention mechanism comprising a conicalsurface, or tapered locking pin, located at an engagement end of theguard positioning mechanism 50 and which is slidably positioned within acollet-like guard opening, described in greater detail below. Themechanical engagement between the positioning mechanism 50 and guard 30allows the positioning mechanism 50 to control the slidable movement ofthe guard 30 between extended and retracted positions. External controlof the guard positioning mechanism 50 is directed by the user via theraised protrusion 58 which extends from within the hollow chamber of thebody 20 via channel 28. The ease of control allows the user one fingercontrol of the positioning mechanism and the attached guard. The raisedprotrusion 58 can also be cantilevered to provide a user operable lockto further prevent undesired movement of the positioning mechanism 50,as described in greater detail below in reference to FIGS. 8G through8L.

As shown in greater detail in FIG. 6, each position of the guard 30 ismaintained by an engagement between a leaf spring 52, located within abody cavity of the guard positioning mechanism 50, and either a first orsecond detent 54 and 56 located in the lower body contour wall 24. Theguard positioning mechanism 50 is substantially hollow and contains aleaf spring 52 which is oriented within the guard positioning mechanism50 with an exposed spring apex extending from the guard positioningmechanism 50 via an opening 60. The spring apex extending from opening60 firmly presses against the lower body contour wall 24 when slidingbetween extended and retracted positions. The lower body contour wall 24includes a first and second detent 54 and 56, located at oppositepositions within the substantially hollow chamber such that the leafspring engages the first detent 54 when the guard positioning mechanism50 is in a fully retracted position, and engages the second detent 56when the guard positioning mechanism 50 is in a fully extended position.Slidable movement of the guard positioning mechanism 50 betweenpositions through the use of a prevailing force is opposed with a slightresistance created by the leaf spring 52 contact with the lower bodycontour wall 24 between detents. As shown in greater detail in FIG. 3C,the path traveled by the leaf spring 52 between detents can also beprovided as a flattened surface 27 on an inside radius of the lower bodycontour wall 25. To ensure consistent spring/wall contact, the surface27 can be flattened (to lower the surface) or include one or more ribs(not shown) to raise the surface 27, such that the spring 52 maintains aconstant deflection when moved between detent openings, regardless ofchanges in the contour wall 25. The slight resistance provided allowsthe guard 30 to maintain a position when the user releases the externalcontrol 58, and prevents the guard from freely sliding.

As shown in FIG. 5A, the guard 30 extends between a generally circularcross section at a proximal end, and a generally semicircular crosssection at an enlarged distal end. The guard is not fully circular alongits entire length due to the need to surround the molded attachment ofthe holder 26 and the blade 40, which is in rigid attachment to the bodyvia the lower body contour wall 24. Therefore the guard 30 includesopposite engagement and shielding ends. At the engagement, or proximalend, the guard has a generally circular cross section and is sized toslidably fit within the hollow chamber within the body 20, andmechanically engage the guard positioning mechanism 50 which directs andcontrols the travel of the guard 30 between a fully extended and fullyretracted position as described above. The engagement end of the guard30 is described in greater detail below.

The shielding, or distal end of the guard 30 shown in FIG. 5A, has agenerally semicircular cross section and is sized to extend and retractthrough the semicircular distal opening provided by the body 20. Anenlarged semicircular area, as also shown in FIG. 4, is provided at theextreme end of the distal end of the guard 30 to provide adequateclearance of the blade 40 when the guard 30 is fully extended.Additionally, as noted above, the enlarged semicircular area provided atthe extreme distal end of the guard 30 remains external to the body 20when the guard is fully retracted, and is rigid enough to provideadditional control and blade orientation with one or more fingers of theuser if so desired.

As shown in FIGS. 5B and 5C, the engagement, or proximal end of theguard 30, includes a pushback prevention mechanism comprising acollet-like coupling mechanism having four flanges 34 a, 34 b, 34 c and34 d, to engage the tapered locking pin 62 located at the engagement endof the guard positioning mechanism 50. As shown in FIGS. 5D and 5E, theengagement end of the guard positioning mechanism 50 includes a pushbackprevention mechanism comprising a tapered locking pin 62 having foursurface quadrants 62 a, 62 b, 62 c, and 62 d. The coupling mechanism ofthe guard 30 engages the four surface quadrants 62 a, 62 b, 62 c, and 62d of the tapered locking pin 62 using the four flanges 34 a, 34 b, 34 cand 34 d extending from the engagement end of the guard and surroundinga mating opening for the locking pin 62. Flanges 34 a and 34 c arelocated on opposite sides of the mating opening and are used to engagesurface quadrants 62 a and 62 c of locking pin 62 to achieve mechanicalengagement. Flanges 34 b and 34 d are also located on opposite sides ofthe mating opening and are used to engage surface quadrants 62 b and 62d of locking pin 62 to achieve pushback prevention engagement.

Mechanical engagement between guard positioning mechanism 50 and theguard 30 is shown in FIGS. 5A-5E and 6. FIG. 6 is an enlargedcross-sectional view showing the locked engagement between flanges 34 aand 34 c, and pin quadrants 62 a and 62 c. FIG. 7 is an enlargedcross-sectional view rotated 90 degrees relative to the view of FIG. 6,and showing the potential for engagement between flanges 34 b and 34 d,and pin quadrants 62 b and 62 d.

As shown in FIGS. 5 and 6, the locking pin 62 is inserted into thecoupling mechanism of the guard 30 until locked into place by lockingflanges 34 a and 34 c. To engage the guard 30 with the guard positioningmechanism 50, the locking pin 62 is inserted into the four lockingflanges 34 a, 34 b, 34 c and 34 d extending from the body of the guard30. The locking pin 62 is tapered along quadrants 62 a and 62 c,allowing an inner lip 32, located about the inside circumference of twolocking flanges 34 a and 34 c, to displace the flanges outward until theinner lip 32 is disposed into the groove 64 near the base of the lockingpin 62, locking the guard into place. When fully engaged, the inner lip32 engages the groove 64 located about the outside circumference of thelocking pin 62, preventing the separation of guard 30 and guardpositioning mechanism 50. The two locking flanges 34 a and 34 c are madeof a material sufficiently pliant to allow displacement outward due tothe insertion of locking pin 62, yet maintain engagement between theinner lip 32 and groove 64 during movement of the guard positioningmechanism 50.

Pushback prevention engagement between guard positioning mechanism 50and the guard 30 is shown in FIGS. 5A-5E and 7. When engaged and fullyextended, additional movement of the guard 30 and guard positioningmechanism 50 toward one another will engage the pushback preventionmechanisms incorporated into the coupling mechanism components describedabove. Travel of the guard 30 toward a stationary guard positioningmechanism 50 indicates that a force, not properly originating from theuser, is acting in a manner to retract the guard. Such forces can resultfrom a number of causes, including external forces applied to the guardwhen fully extended. Examples include instances where the extended guard30 is pushed, bumped or struck, or when the handle 10 is dropped on theend from which the guard 30 extends. Such forces could result in theguard partially retracting and exposing part or all of the blade 40. Toprevent this, the pushback prevention mechanism is engaged when theguard 30 is fully extended and an external force is applied to the guardwhich would tend to force the guard from the fully extended positionagainst the resistance of the guard positioning mechanism 50.

As shown in FIGS. 5A-5E and 7, the locking flanges 34 b and 34 dextending from the body of the guard 30 each include an inner ramp 36,which engages the surface quadrants 62 b and 62 d of the locking pin 62of the guard positioning mechanism 50 when the guard 30 is moved towardsthe guard positioning mechanism beyond the locking point describedabove. Quadrants 62 b and 62 d include a slight flat along the taper ofthe pin such that in a normal, engaged position, the inner ramp contacts36 do not displace the flanges 34 b and 34 d. However, while fullyextended, if there is an external force applied to the guard 30, forcingthe guard towards the guard positioning mechanism 50, the pin surfacequadrants 62 b and 62 d engage the ramps 36 and the locking flanges 34 band 34 d are displaced in an outward direction, against the inner wallsof the hollow chamber within the body 20. As the flanges 34 b and 34 dare displaced, each contacts a groove 38, located along the inner wallof the chamber. The flanges 34 b and 34 d, once fully displaced withinthe groove 38, travel along the groove a minute distance untilcontacting a shoulder at the end of each groove, stopping any furthertravel of the flanges in a rearward direction, thus preventing anynoticeable retracting movement of the guard 30 from the fully extendedposition.

Flanges 34 a and 34 c also work in cooperation to achieve the pushbackprevention function. The groove 64 which is engaged by the inner lip 32of flanges 34 a and 34 c, has a sufficient width to allow the inner lipto travel slightly rearward during engagement of the pushback preventionmechanism, such that the flanges 34 a and 34 c do not interfere with thefunction of the pushback prevention mechanism of flanges 34 b and 34 d.If the inner lip 32 were not allowed to travel in the groove 64, anyrearward force on the guard 30 would displace the guard positioningmechanism 50 before the pushback prevention mechanism could engage.

Yet another cooperation feature between flanges 34 a and 34 c, and thepushback prevention mechanism can include an inner surface of flanges 34a and 34 c each including a slight relief (not shown), which preventsthe flanges from possibly displacing slightly outwards when inner lip 32is engaged in the groove 64, due to flange thickness and the surface ofpin 62. Likewise, flanges 34 b and 34 d are slightly shorter thanflanges 34 a and 34 c, allowing the mechanical engagement to occurwithin the chamber housing without interference.

The resistance provided by the leaf spring 52 engagement with the fullyextended detent slot 56 is sufficient to hold the guard positioningmechanism 50 in place when an external force is applied to the fullyextended guard 30. The guard positioning mechanism 50 remains inposition as the guard 30 is slightly displaced rearward activating thepushback prevention mechanism incorporated into the coupling mechanismas described above. In this embodiment, the slight rearward displacementprior to full activation of the pushback prevention mechanism isnegligible.

In a second version of the first embodiment, the guard positioningmechanism 50 of the user actuator can be constructed with an integralcantilever beam spring along a bottom surface of the mechanism body toprovide the spring biasing mechanism forcing detent engagement. In thisversion as shown in FIGS. 8A through 8F, the guard positioning mechanism50 has an integral cantilever beam 70 along a bottom surface, secured ata first end and flexing at an opposite end, and upon which an inclinedprojection 72 is used to provide the spring biasing mechanism. Thisplastic molded spring can be used to replace the leaf spring 52 andmaintain each position of the guard 30 by an engagement between themolded spring and the first or second detent 54 and 56 located in thelower body contour wall 24.

In this second version, the guard positioning mechanism 50 includes atleast one inclined projection 72, wherein the incline (i.e., 45 degrees)is provided to allow easy entry and removal from the detents. Theintegral cantilever beam 70 firmly presses the projection 72 against thelower body contour wall 24 when sliding between extended and retractedpositions. As noted above, the lower body contour wall 24 includes afirst and second detent 54 and 56, located at opposite positions withinthe substantially hollow chamber such that the projection 72 engages thefirst detent 54 when the guard positioning mechanism 50 is in a fullyretracted position, and engages the second detent 56 when the guardpositioning mechanism 50 is in a fully extended position. Slidablemovement of the guard positioning mechanism 50 between positions throughthe use of an applied force on the external control 58 is opposed by aslight resistance created by the projection 72 in contact with the lowerbody contour wall 24. The slight resistance provided allows the guard 30to maintain a position when the user releases the external control 58,and prevents the guard from sliding freely.

When constructed having similar spring characteristics, the use of theintegral cantilever beam 70 and the inclined projection 72 eliminatesthe need for a metal spring component. The spring biasing mechanismtherefore becomes part of the user actuator (i.e., raised operatorcontrol 58 and guard positioning mechanism 50), and all can be made fromone piece of material. This reduces variability in the “feel” whenmoving the guard positioning mechanism 50 between positions (i.e., inand out of detent engagements). In the above embodiments, when the metalleaf spring component 52 is assembled into the guard positioningmechanism 50, the dimensions of the metal spring component can bealtered due to the nature of the assembly method required. Additionally,the metal leaf spring can have a reduced cycle life relative to theplastic molded spring, and can deform after few detent engagements.

Combining the spring biasing mechanism and the user actuator into one,thus eliminating one of the two parts, allows for tighter tolerancesbetween the remaining components (i.e., detent and spring biasingmechanism). Furthermore, the variability incurred as part of theassembly method between the metal leaf spring component and the useractuator is also removed. The tighter tolerances and removal of theassembly method added variability ensures smooth and consistent detentengagement. As with the above embodiments, the smoother detentengagements also provide feedback to the user through an audible clickand a mechanical snap that can be felt through the user actuator.

The integral cantilever beam 70 and inclined projection 72 can bemodified in shape and form, and still act as the spring biasingmechanism. For example, in yet another version the cantilever spring 70and inclined projection 72 can be molded into the lower body contourwall 24 (i.e. handle base) and the detents 54 and 56 placed into theguard positioning mechanism 50 of the user actuator, thereby reversingthe locations of these two features.

The guard positioning mechanism 50 of the user actuator can also beconstructed with an integral cantilever beam along a top surface of themechanism body to provide an upwardly biased, user operable lock forengagement with a detent, groove, or slot 84 provided in the upper bodycontour wall 22. FIG. 8G is an exploded perspective view of anotherembodiment of the present invention including such a user operable lock.In this embodiment, as shown in FIGS. 8G through 8L, the guardpositioning mechanism 50 has an integral cantilever beam 80, secured ata first end and flexing at an opposite end upon which an inclinedprojection 82 is used to provide the upwardly biased, user operable lockmechanism. FIG. 8H is a side cross-sectional view of the guardpositioning mechanism and additional user operable lock in a lockedposition. FIGS. 81 through 8L are views of the guard positioningmechanism and additional user operable lock of FIG. 8G. Specifically,FIG. 8I is a cross-sectional view of the guard positioning mechanism 50and user operable lock, and FIG. 8J is a perspective view of the guardpositioning mechanism 50 and user operable lock. FIG. 8K is a top viewof the guard positioning mechanism 50 and user operable lock, and FIG.8L is a cross-sectional view taken along line 8L of FIG. 8K. In thisembodiment, the plastic molded beam 80 can be used to engage theinclined projection 82 with the slot 84, and maintain the forward, orextended position of the guard positioning mechanism 50 until releasedby the user. In doing so, the shield can be substantially protected frombecoming accidentally displaced during shipping or during mishandlingwhen packaged and exposing the blade.

In this embodiment, the guard positioning mechanism 50 includes at leastone inclined projection 82, wherein the incline or sloped wall 86 (i.e.,30 degrees from the horizontal) is provided to allow easy entry into theslot 84. The perpendicular or vertical wall 88 of the inclinedprojection 82 is provided to engage a surface of slot 84, preventingrearward motion of the positioning mechanism 50 until a user depressesthe raised operator control 58 which is now disposed on the integralcantilever beam 80, thereby forcing the integral cantilever beam 80downward and disengaging the inclined projection 82 from the slot 84.Once disengaged, the user can retract the positioning mechanism 50 andguard 30. To activate the user operable lock mechanism, the useradvances the positioning mechanism 50 and guard 30, which also serves toadvance the integral cantilever beam 80 and the inclined projection 82.The leading or sloped edge 86 increasingly loads and deflects theintegral cantilever beam 80 when contacting the upper body contour wall22 until the positioning mechanism 50 is in the proper position for theinclined projection 82 to “snap” into place in the slot 84. Although theupper body contour wall 22 is shown in this example having a slot, anyrecess, cavity, notch, opening or other structure sufficient to captureand release the inclined projection 82 can be used.

The integral cantilever beam 80 firmly presses the projection 82 againstthe upper body contour wall 22 when sliding the positioning mechanism 50near the fully extended position. In this version, the upper bodycontour wall 22 includes the slot 84, such that the projection 82engages the slot 84 when the guard positioning mechanism 50 is in afully extended position. Slidable rearward movement of the guardpositioning mechanism 50 is then opposed by the projection 82 in contactwith the slot 84 of the upper body contour wall 22. This locked positionallows the guard positioning mechanism 50 to maintain its position evenin cases where the device is struck at the proximal end, rather thanbeing struck at the distal, or guarded end. Although the embodimentshown in FIGS. 8G through 8L has the integral cantilever beam 80extending toward the distal end of the device, the slot 84 can bedisposed at any number of positions such as toward the proximal end ofthe device, and the beam and/or projection can therefore, also beprovided extending toward the proximal end of the device, or anywherealong the sides of the positioning mechanism 50.

As noted above, the pushback prevention mechanism of FIGS. 5A through5E, 6 and 7, substantially prevents rearward movement of the fullyextended guard 30 when struck, bumped or contacted in any way at thedistal end of the device. Further, the user operable lock mechanismsubstantially prevents the shield from becoming accidentally displacedduring shipping or during mishandling when packaged. However, whenstruck at the proximal end of the device, the mass of the positioningmechanism 50 can in some cases, force the positioning mechanism 50rearward due to inertia. In this case, the pushback prevention mechanismmay not engage, as the pushback prevention mechanism functions mosteffectively when the guard 30 is struck, bumped or contacted and isforced rearward toward the stationary positioning mechanism 50. If thepositioning mechanism 50 is itself moving rearward, as can be the casewhen the device or its package is struck at the proximal end, thepushback prevention mechanism alone may not sufficiently maintain theguard 30 in a fully extended position. However, when the positioningmechanism 50 is provided with the user operable lock as described above,a degree of redundancy is designed into the device. This eliminates theundesired movements of the positioning mechanism 50, as the useroperable lock incorporates a positive catch that provides maximumholding force along the long axis of the device. The locking contactsurface between projection 82 and the slot 84 is provided at asubstantially 90° angle relative to the force vector imposed during aproximal end impact.

Undesired movement of the positioning mechanism 50 can be furtherprevented through packaging techniques. For example, the device can berotated and packaged in a “tray” or fitted package, such that thepositioning mechanism 50 is prevented from moving by the package itself.The package can also be constructed using clear “blister pack”technology or include a band around the handle of the device, whichtightly contacts the device. This contact, specifically contact betweenpackaging and the raised operator control 58, blocks any movement of thecontrol 58, thereby preventing movement of the positioning mechanism 50.The device can also be positioned within the package such that theproximal end of the device is near the package end having the largestarea of material (i.e., opposite the end to be opened). This additionalmaterial, or added padding, can act as a cushion for the proximal end ofthe device when the package is struck or bumped. Still other packagingtechniques can include shipping the device unguarded, foam packaging theunguarded device, and/or including labeling to note that drops orabnormal uses/shocks can impair the safety of the device.

As noted above, the undesired movement of the positioning mechanism 50can be prevented through design techniques. For example, returning toFIG. 3A, the undesired movement of the positioning mechanism 50 can besubstantially prevented through the engagement between the spring 52,located within a body cavity of the guard positioning mechanism 50, andthe first and second detent 54 and 56 located in the lower body contourwall 24. Similarly in FIG. 8A, the undesired movement of the positioningmechanism 50 can be substantially prevented through the engagementbetween the integral cantilever beam 70 and inclined projection 72, andthe first and second detent 54 and 56 located in the lower body contourwall 24. In each case, when kept in a position, such as in a guardedposition, the components can take a “set” in that position to furtherprevent movement of the guard positioning mechanism 50. Where furtherprotection from undesired movement is required, the user operable lockcan be provided. In that case, the undesired movement of the positioningmechanism 50 can be substantially prevented through the engagementbetween the integral cantilever beam 80 and inclined projection 82, andthe slot 84 located in the upper body contour wall 22.

In yet another technique in which undesired movement of the positioningmechanism 50 can be prevented, a “flaring lock”, such as that providedby the pushback prevention mechanism described above in connection withFIGS. 5A through 5E, 6 and 7, can be inverted and provided on thepositioning mechanism 50. When the user slides the raised operatorcontrol 58, the movement collapses a number of flared elements (whichare biased outward in a relaxed position to secure the positioningmechanism 50), thereby releasing the positioning mechanism 50 formovement.

In still another technique in which undesired movement of thepositioning mechanism 50 can be prevented, a shock absorbing tip can beprovided on the end of the device (i.e., a rubber bumper), or providedon the end of a pin or rod, as described in greater detail below withreference to FIG. 13A.

In another embodiment of the present invention, a drop-force operablelock can be provided to substantially prevent the guard from becomingaccidentally displaced and exposing the blade when a force is applied tothe proximal end of the device. In a shock absorbing technique, a pin orrod can be attached to the positioning mechanism 50 and protrude out thebase, or proximal end of the device as shown in FIG. 13A. FIG. 13A is across-sectional view of another embodiment of the present invention witha drop-force operable lock. In FIG. 13A, a pin 90 is provided through anopening 92, and is flush with the proximal end when the guard 30 isforward, and extends beyond the proximal end when the guard 30 isretracted. Should the proximal end of the device be struck or bumpedwhen the guard is forward, the pin or rod transmits the impact force tothe positioning mechanism 50 to maintain the positioning mechanism 50and the guard 30 in an extended position. The pin or rod 90 contacts theback of the positioning mechanism 50 via a fitting 94, such as athreaded fitting, and can move an equal length to guard travel. In sucha configuration, when the guard 30 is retracted, the pin 90 is in the“out” position, and when the guard 30 is extended and locked, the pin 90is in the “in” position. A shock absorbing tip 96 can be provided on theend of the pin 90, and can have any number of shapes, such as tips 97and 98 shown in FIGS. 13B and 13C, respectively. The tip can be made ofa rubber eraser-like material added to proximal end of the devicehandle, and can be angled, similar to the rubber tips found on theproximal end of a toothbrush.

In yet another technique to prevent undesired movement of thepositioning mechanism 50, a compression spring can be added to bias loadforward during sudden movement, such as when the device is dropped. Instill another technique to prevent undesired movement of the positioningmechanism 50, a rubber grommet can be provided about the positioningmechanism 50 to engage an inner surface of the device and stabilize themechanism and resist movement.

In still another technique to prevent undesired movement of thepositioning mechanism 50, a mechanical fuse can be provided to disablethe device if the device is dropped. A twist lock feature can also beadded to the positioning mechanism 50, such that a movement of thepositioning mechanism 50 would require a forward force, as well as aforce to one side (i.e., an “L”-shaped or twist movement). This mayrequire changes to the positioning mechanism 50, guard 30 and base. AnO-ring can also be provided as a stop and/or shock absorber for thepositioning mechanism 50.

In still another technique to prevent undesired movement of thepositioning mechanism 50, the spring 52 or inclined projection 72 can bemodified to include a vertical wall in addition to the contour (in thecase of the spring 52) and the angles (typically 30° to 45° in the caseof the inclined projection 72). Therefore, to release the newly addedvertical wall of the spring 52 or inclined projection 72 from the firstor second detent 54 and 56 located in the lower body contour wall 24,the user would be required to press against the spring 52 or inclinedprojection 72 in an upward motion with a finger from the base, raisingthe spring 52 or inclined projection 72 into the contoured or angledsection. The user could then pull back on the positioning mechanism 50as normal.

In still another technique to prevent undesired movement of thepositioning mechanism 50, the engagement between the positioningmechanism 50 and the guard (i.e., the pushback prevention mechanism),can be provided with a degree of clearance or free movement, to allowthe positioning mechanism 50 to move during an impact, but not pull theguard 30. Care is required to ensure that the additional movement spacedoes not prevent the shield tabs to miss the detents in the handlehalves (i.e., the function of the pushback prevention mechanism). Thiscan possibly be overcome by adding mass to the guard, such as a weight(i.e., ball bearing), thereby making the shield tabs flare earlierduring an impact or fall.

In still another embodiment, a fully circular guard may also be used toshield the exposed blade. In another embodiment of the presentinvention, the guard is fully circular at the distal end, which allows alarger portion of the guard to remain exposed when fully retracted. FIG.9A is a perspective view of an embodiment of the present invention 100with the guard 130 in a retracted position to expose a blade 140 foruse. The guard 130, when in the retracted position, forms a smooth,uninterrupted handle surface between distal and proximal endssubstantially as described in the first embodiment. When not in use, theguard 130 can be extended, as shown in FIG. 9B, to safely shield theblade 140.

FIG. 10 is an exploded perspective view of the embodiment of FIG. 9A.The view of FIG. 10 includes a first and second body contour wall 122and 124, formed to assemble as a handle body 120 and define asubstantially hollow chamber within the body 120 to house a concealableportion of the guard 130. The first and second body contour walls 122and 124 each provide a recess, which when assembled, creates a slot 128extending rearward from the distal end and accessing the chamber toallow protrusion of a raised operator control 158 for the guard 130. Thedistal end of the first and second body contour wall 122 and 124 alsoincludes an outer surface having a dimpled texture, extending from thedistal end to a point slightly before the midpoint of the access slot128. Additionally, as shown FIGS. 9A and 9B, the outer circumferencesurface area of an exposed portion of guard 130 also includes a dimpledtexture, such that when fully retracted, the dimpled texture surfacearea is unbroken about the distal end of the body 120.

The distal ends of both the first and second body contour wall 122 and124 further include a reduced outside diameter for receiving the exposedportion of guard 130. Specifically, as the guard 130 is slidablyretracted, the fully circular exposed portion of guard 130 is receivedby the reduced outside diameter of the first and second body contourwall 122 and 124, until reaching a shoulder at the fully retractedposition. Seating the guard 130 against the shoulder of the reducedoutside diameter forms the smooth, uninterrupted handle surface betweendistal and proximal ends described above.

In the embodiment of FIG. 10, the guard 130 is controlled to travelbetween a fully extended and fully retracted position via an externalprotrusion 158 accessed through channel 128 in a manner substantially asdescribed in the embodiment of FIG. 3A. As shown in FIGS. 10 and 11,each position is maintained by an engagement between a spring 152 withina body cavity of the guard positioning mechanism 50 and either a firstor second slot 154 and 156, provided along rails at either side of thehollow chamber within the body 120. The chamber, slots and rails areformed as described below, and serve to provide a slidable engagementsurface for the guard to travel between fully extended and fullyretracted positions.

As shown in FIGS. 10 and 11, the first and second body contour wall 122and 124 assemble to define a substantially hollow chamber within thebody 120 to house the guard 130 which contains a spring 152 mountedbeneath a saddle 160 that is driven between rails on either side of thechamber. The guard 130 includes a fully circular distal end, provided toshield the blade 140 when fully extended. An elongated member 132extends rearward from the fully circular distal end, and provides aplatform supporting a saddle 160, a plate 136, an external protrusion158 and a contoured end 134.

As shown in FIG. 11, each body contour 122 and 124 provides a first andsecond rail 162 and 164, along the inner wall of the chamber. The firstrail 162 is provided to engage the spring 152, as described in greaterdetail below. The second rail 164 is provided to engage the saddle 160,and maintain saddle alignment between fully extended and retracted guardpositions.

The first rail 162 is provided between saddle 160 and spring 152. Thespring 152 is mechanically attached to the bottom of the saddle 160 andincludes an extension having a 90 degree angle oriented to firmly pressagainst the upper surface of the first rail 162 when sliding betweenextended and retracted positions. The upper surface of the first rail162 of each contour wall 122 and 124 includes a first and second slot154 and 156, located at opposite positions along the substantiallyhollow chamber such that the spring 152 engages the first slot 154 whenthe guard 130 is in a fully retracted position, and engages the secondslot 156 when the guard is in a fully extended position. Slidablemovement of the guard 130 between positions is opposed with a slightresistance created by the spring 152 contact with the rail surface oneither side of the chamber. Additional features can be provided toprevent possible twisting of the fully circular distal end of the guard130 when fully extended. As shown in FIG. 10, the second body contourwall 124 can include a recessed groove 166 extending along the surfaceof the distal end beneath the elongated member 132. A plate (not shown),extending below the elongated member, can be used to slidably engage therecessed groove 166 of wall 124, providing alignment and support for theelongated member 132 and the fully circular distal end of the guard 130when traveling between fully extended and fully retracted positions.

Once the spring 152 engages either the first or second slot, the guard130 is locked in place. To disengage the spring 152 requires the user toapply slight perpendicular pressure to the external protrusion 158 untilthe spring 152 is disengaged from the slot, and thereafter, a parallelforce can be used to slidably move the guard 130 to a new position. Asnoted above, the spring 152 is oriented to firmly press against thesurface of the first rail when sliding between extended and retractedpositions, and maintain a position in the first or second slot when atextended or retracted positions. Therefore, to allow the application ofslight perpendicular pressure required to disengage the spring 152 fromeither slot 154 or 156, the guard 130 includes the elongated member 132extending into the chamber and contacting a surface via a contoured end134. The guard 130 also includes a slight notch 138 at a point betweenthe saddle 160 and a plate 136 extending downward and contacting thespring 152.

To disengage the spring 152 from either slot 154 or 156, a slightperpendicular pressure applied to the external protrusion 158 istransferred to the elongated member 132. The contact at the contour 134,and the slight notch at 138, allows the perpendicular pressure todisplace the plate 136 downward, forcing the spring 152 from the slot.The plate 136 is slightly narrower than the spring 152, therefore theplate can freely move between rails and deflect the wider spring 152from contact with rail 162. As with the embodiment of FIG. 3A, theprotrusion 158 can provide simple and safe one finger control of theguard 130. Further, a user operable lock and a drop-force operable lockcan be provided with the embodiment of FIG. 10 to prevent accidentalretraction of the guard from the fully extended and guarded position insubstantially the same manner as described above.

In a modified version of the embodiment of FIG. 10 (not shown), thefirst and second body contour wall assemble to define a substantiallyhollow chamber within the body to house the guard which contains aspring mounted beneath a saddle that is driven between rails on eitherside of the chamber substantially as described above. However, in thisversion, the spring is oriented to contact the bottom of the chamber andfirmly press the saddle against the surface of at least one railprovided when sliding between extended and retracted positions. Eachcontour wall includes a first and second slot, located at oppositepositions along at least one rail within the substantially hollowchamber such that the saddle, under pressure from the spring, engagesthe first slot when the guard is in a fully retracted position, andengages the second slot when the guard is in a fully extended position.Once the saddle engages either the first or second slot, the guard islocked in place. To disengage the saddle requires the user to applyslight perpendicular pressure to the external protrusion until thesaddle is disengaged from the slot, and thereafter, a parallel force canbe used to slidably move the guard to a new position.

In another embodiment of the present invention, the slidable movement ofthe guard positioning mechanism is achieved using a plunger mechanism,as often associated with any of several ballpoint pen mechanisms thatadvances a pen tip through the push of a button. FIGS. 12A and 12B areperspective views of an embodiment of the present invention with aplunger type operator control and the guard in an extended and retractedposition, respectively. Such mechanisms 255 typically involve a useractivated plunger to advance a pen tip outward or to retract a pen tipinward in a longitudinal direction. The use of a pen mechanism at theproximal end of the device can provide an alternative to the side slotdescribed in regards to the above embodiments. This would allow furthervariations in the single handed use of the embodiments described above.

Such a pen mechanism would preferably utilize features similar to thosein current pens to move the blade guard back and forth, as opposed toextending and retracting a pen tip. A user actuator can be located onthe proximal end of the device that functions like a pen mechanism, i.e.to click the guard 230 in or out. Specifically, the mechanism couldinclude a simple, single cylindrical member 250 extending from theproximal end opening 254 along the axis of the device body 220, andoperate in a click-in and click-out fashion with an extension/retractionmechanism 255 as known to those skilled in the art. Alternatively, themechanism could include a cylindrical member extending from the proximalend along the axis of the device and being divided into two or moremembers, or segments, 256 and 258 as shown in FIG. 12C. The dividedmembers, when together, form the single cylindrical member; however eachmember can move relative to the others and provide an action unique tothe movement of the particular divided member. Related divided functionmechanisms can be found in multi-colored ballpoint pen mechanisms, whichinclude different push button segments to extend different colors of pentips from a single device.

In this example, various guards could be fabricated to fit inside and/oroutside the body and/or chamber of the handle and still achieve thedesired coverage of the blade. By disposing the guard partially insideand/or outside the device, the handle or body of the device can beconstructed with a smaller diameter, or allow for the guard to bettershield the blades described above or other blade geometry.

The guards could further comprise various shapes which can provide bladeshielding at various places or of various strengths. Specifically,different guard shapes may provide different strength characteristics,and further allow the guard to withstand higher forces. These may alsoallow for a smaller guard, or enlarged guard distal end, therebyminimizing visual interference with the blade while providing maximumprotection from blade contact resulting in a blade stick. Such a guarddesign can be either completely inside, outside or a combination ofboth, and the guard and enlarged guard distal end can be either open orclosed, and can achieve full-circumference protection or providealternative means to shield a blade depending on blade design. Inexamples which provide a semi-circular guard, the guard and enlargedguard distal end can still include other shapes, such as, but notlimited to, triangle, square and/or box shapes, and still other shapeshaving multiple facets or sides, all with or without a circular orradius cross section, but which still provide shielding for blades ofdifferent geometries.

Returning to FIGS. 12A and 12B, the spring biasing mechanism thatprovides detent engagement within such a pen mechanism can include anynumber of configurations, such as the leaf spring and a cantilever beamdescribed above, or a compression/extension spring. In still anotherexample, the spring, such as the leaf spring, could be replaced withanother spring biasing mechanism forcing detent engagement. In eachexample, the spring could provide a sufficient resistive force necessaryfor the guard function. In the embodiments of the present inventiondescribed above, the guard and enlarged guard distal end can beconfigured to withstand forces up to 3 lbs. in one example. Where such aspring biasing mechanism is used, the required applied force wouldtypically be equal to or greater than the force which the guard canwithstand. In yet another example, the spring biasing mechanism may beused to reduce the force required to move the guard back and forth, orto strengthen the guard design in each embodiment described above.

Unlike prior blade shielding mechanisms, embodiments of the presentinvention can withstand an inadvertent force. Such protection can beprovided by utilizing a leaf spring or beam and detents to fix the guardin the extended and retracted position, by utilizing a pushbackprevention mechanism and a user operable lock to prevent accidentalretraction from the fully extended position, and by utilizing adrop-force operable lock to transfer any drop-force to the guard toprevent guard movement. These embodiments do not disengage or allow theguard to move from the shielding state to the non-shielding state by anyreasonable inadvertent force applied longitudinally to the guard. Eachembodiment therefore is able to implement a lock-out feature.

Embodiments of the present invention can be constructed of any suitablematerial, including a number of materials which can be autoclaved forrepeated use. For example, where the embodiments are provided with metalblades and suitable body materials, multiple uses are possible usingsteam autoclave processes. In such examples, a preferred blade 40 andspring 52 material includes stainless steel (for metal spring versionsonly), and the body 20 and guard positioning mechanism 50 can beconstructed of polyetherimide. The guard 30 can be constructed oftransparent or opaque polycarbonate. Where the leaf spring 52 is omittedand replaced with an integral cantilever beam 70 and inclined projection72, the beam and projection can also be constructed of a polyetherimide.Additionally, where the user operable lock is provided, the integralcantilever beam 80 and inclined projection 82 can also be constructed ofa polyetherimide. The drop-force operable lock can be constructed of anyrigid rod 90 and resilient rubber-like material for the tip 96.

Other blade materials can also be used, including silicon and diamonds,and the body 20 can be constructed of autoclave intolerant materials,such as high impact polystyrene. The use of high impact polystyrene willresult in the substantial destruction of the device when autoclaved,thereby preventing reuse. In such applications, the leaf spring 52 canbe constructed of stainless steel (for metal spring versions only), andthe guard positioning mechanism 50 and guard 30 can be constructed ofpolyetherimide and polycarbonate, respectively.

Although only a few exemplary embodiments of the present invention havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

What is claimed is:
 1. A method for shielding a knife blade in a safetyhandle having a handle body with a distal end, a proximal end and a slotextending along a portion of a longitudinal handle body axis and havingat least one detent adjacent to the slot, the safety handle also havinga knife holder for carrying the knife blade, and a guard positioningmechanism movably disposed within the handle body, the guard positioningmechanism having a guard portion, the method comprising the steps of:depressing a user control mechanism disposed upon a cantilever, whereinthe cantilever is secured only at its proximal end to the guardpositioning mechanism, the user control mechanism extending outwardlyfrom the handle body via the slot; wherein the cantilever releasablyengages the detent to releasably secure at least one of the knife holderand the guard portion at a position with respect to the handle body, anddepressing the user control mechanism releases the cantilever from thedetent to allow relative movement between the guard positioningmechanism and the handle body; and moving the user control mechanismalong the slot to selectively cover or expose the knife blade relativeto the guard portion.
 2. A method for shielding a knife blade in asafety handle as claimed in claim 1, wherein the cantilever isresiliently biased toward the slot when the user control mechanism isdepressed.
 3. A method for shielding a knife blade in a safety handle asclaimed in claim 1, wherein the cantilever comprises a projection forengagement with the detent to substantially secure the user controlmechanism in one of a fully extended position and a fully retractedposition.
 4. A method for shielding a knife blade in a safety handle asclaimed in claim 1, wherein the detent comprises at least one of arecess, a cavity, a notch or an opening in the handle body.
 5. A methodfor shielding a knife blade in a safety handle as claimed in claim 1,wherein the guard portion is constructed of a transparent material.
 6. Amethod for shielding a knife blade in a safety handle as claimed inclaim 1, wherein the guard portion is constructed of an opaque material.7. A method for shielding a knife blade in a safety handle having ahandle body with a distal end, a proximal end and an opening in aportion of the handle body and having at least one detent in the handlebody, the safety handle also having a knife holder for carrying theknife blade, and a guard positioning mechanism movably disposed withinthe handle body, the guard positioning mechanism having a guard portion,the method comprising the steps of: depressing a user control mechanismdisposed upon a cantilever, wherein the cantilever is secured only atits proximal end to the guard positioning mechanism, the user controlmechanism extending outwardly from the handle body via the opening;wherein the cantilever releasably engages the detent to releasablysecure at least one of the knife holder and the guard portion at aposition with respect to the handle body, and depressing the usercontrol mechanism releases the cantilever from the detent to allowrelative movement between the guard positioning mechanism and the handlebody; and moving the user control mechanism to selectively cover orexpose the knife blade relative to the guard portion.
 8. A method forshielding a knife blade in a safety handle as claimed in claim 7,wherein the cantilever is resiliently biased toward the opening when theuser control mechanism is depressed.
 9. A method for shielding a knifeblade in a safety handle as claimed in claim 7, wherein the cantilevercomprises a projection for engagement with the detent to substantiallysecure the user control mechanism in one of a fully extended positionand a fully retracted position.
 10. A method for shielding a knife bladein a safety handle as claimed in claim 7, wherein the detent comprisesat least one of a recess, a cavity, a notch or an opening in the handlebody.